Mass spectrometry is an analytical technique for the determination of molecular weight related information and in some instances structurally significant fingerprint information from molecular fragments, all toward the identification of chemical structures, the determination of the composition of mixtures, and qualitative elemental analysis. In operation, a mass spectrometer generates ions from sample molecules under investigation (the analyte), separates the ions according to their mass-to-charge ratio (m/z), and measures the relative abundance of each ion. In a typical mass spectrometer, the path of travel of the Ions through the mass spectrometer depends on their mass and charge, thus ions are separated based upon their m/z and then detected. The detector within the mass spectrometer produces a relative m/z value along with a measure of signal intensity related to the number of ions of the same m/z value that are detected. A plot of the signal intensity values as a function of the m/z value is known as a mass spectrum.
If the analyte remains intact throughout this process, data obtained will be related to the molecular weight for the entire intact analyte ion. Typically, however, and especially for the case of larger analytes, it is beneficial to obtain data corresponding to the molecular weight of various fragments of the analyte. The resulting spectrum is known as a fragmentation spectrum for the analyte of interest.
Although the fragmentation spectrum can be of interest for a variety of uses, it is often desired to use the fragmentation spectrum as a molecular “finger-print” to identify a compound or compounds of interest that resulted in the fragmentation mixture. Previous approaches have typically involved using the fragmentation spectrum as a basis for hypothesizing one or more candidate compounds. This procedure has typically involved manual analysis by a skilled researcher.
The procedure that involves hypothesizing identification of candidate compounds based on direct analysis of experimental fragmentation spectra is useful in a number of contexts, but also has certain difficulties. For example, manual interpretation of the fragmentation spectra so as to identify unknown analytes is time-consuming, often inaccurate, and highly technical and in general can be performed only by those with extensive experience in mass spectrometry. Reliance on human interpretation often means that analysis is relatively slow and lacks strict objectivity.
Alternatively, it is also possible to utilize a system for correlating fragment spectra from unknown analytes with known compound fragment spectra derived from a library of fragment spectra from previously analyzed known compounds. Such a system may avoid the delay and/or subjectivity involved in hypothesizing or deducing candidate amino acid sequences from the fragmentation spectra.
Although comparing experimental fragment spectra with a database of known compound spectra is an improvement over direct analysis of the experimental spectra, this process can also have certain drawbacks. For example, the database of known spectra must usually be accumulated through mass spectrometry analysis of each of the compounds included in the database. Therefore, establishing the database initially and updating it requires expenditure of time and resources for derivation of the database spectra. Further, it may also be difficult to obtain fragmentation spectra on some compounds desirable to include in the database, if, for example, the compounds could not be readily purified or obtained in sufficient quantities necessary for mass spectrometry. Finally, comparative analysis of experimental fragmentation spectra to the database spectra must be performed, which again requires extensive time and resources. These drawbacks are particularly acute when large numbers of unknown compounds must be identified rapidly, for example, in high throughput screening procedures for identification of potential drug candidates.
Therefore, it would be desirable to quickly and efficiently identify unknown analytes by comparing and matching mass spectrometry fragmentation data with a database of fragmentation spectra from known compounds. It would further be desirable to be able to quickly and efficiently populate the database of fragmentation spectra without necessarily analyzing each compound by mass spectrometry in order to derive the fragmentation spectra.